The present invention relates generally to a digital frequency measurement receiver with means to resolve an ambiguity in multiple frequency estimation, and more particularly to means to resolve two folding frequencies of complex signals.
The following U.S. patents are of interest. U.S. Pat. No. 4,963,816-Tsui et al U.S. Pat. No. 5,099,194-Sanderson et al U.S. Pat. No. 5,099,243-Tsui et al U.S. Pat. No. 5,109,188-Sanderson et al U.S. Pat. No. 2,989,744-Pettit U.S. Pat. No. 3,913,099-Wehner et al U.S. Pat. No. 4,359,735-Lewis et al U.S. Pat. No. 4,816,832-Gold et al U.S. Pat. No. 4,866,449-Gaffney U.S. Pat. No. 5,077,562-Chang et al.
Tsui et al in U.S. Pat. No. 4,963,816 disclose an Instantaneous Frequency Measurement receiver having two delay lines wherein frequency resolution is based on the Chinese Remainder Theorem. The theorem states that if an unknown number X is divided by a number a with a remainder r.sub.1 and also divided by a number b with a remainder r.sub.2, where a and b are relatively prime numbers, the number X can be determined uniquely from a, b, r.sub.1 and r.sub.2 if X&lt;ab. For example, if a=5, b=7, r.sub.1 =2 and r.sub.2 =1, the Chinese remainder gives an X of 22.
Sanderson et al in U.S. Pat. No. 5,099,194 disclose a digital frequency measurement receiver with bandwidth improvement through multiple sampling of real signals. Two sets of uniform samples are used with slightly different sampling frequency, wherein each set is Fourier transformed independently and the frequency of the lowest aliases determined. Unambiguous determination of the signal frequency over a range far exceeding the Nyquist frequency is obtained except at a discrete set of points. Tsui et al in U.S. Pat. No. 5,099,243 disclose a technique for extending the frequency range of a digital frequency measurement receiver, through multiple sampling of complex signals, which employs in-phase and quadrature components of the signal coupled with non-uniform sampling. Each set of complex samples is independently Fourier transformed, and the frequency of the lowest aliases permits unambiguous determination of the signal frequency over a range far exceeding the Nyquist frequency.
Sanderson et al in U.S. Pat. No. 5,109,188 disclose a technique for extending the frequency range of an instantaneous frequency measurement receiver, wherein a power divider is employed with two outputs. One output is supplied to a first A/D converter, and the other output is supplied via a delay device to a second A/D converter. A processor 60 receives the outputs of the two A/D converters 42, 44. The input signal is subjected to a known delay .tau. and both original and delayed signals are sampled simultaneously and Fourier transformed and both the phase and amplitudes calculated.
The Pettit U.S. Pat. No. 2,989,744 describes a false echo transmitter wherein pulses from an enemy radar are delayed in time by a suitable interval and utilized to activate a local transmitter which emits delayed radio pulses and thus to confuse the enemy.
Gold et al U.S. Pat. No. 4,816,832 discloses a continuous repeater target denial device having a receiver 12, RF filters, and transmitter 14. Lines 30 respectively carry a different local oscillator frequency which is of the same order of magnitude as the received radar burst frequency. A recirculation loop 48, a delay device 66, a control circuit 70, and other circuit elements are disclosed. A plurality of filters is provided, each one of them passing the frequency band of the enemy radar signal, so a corresponding one of a plurality of local oscillator frequencies that are all continuously generated can be used to mix with the received signal for circulating in an IF loop. A differential time delay assures that the appropriate local oscillator frequency arrives at the loop down converter prior to or at the same time as the signal. The apparatus also includes an amplitude and doppler offset modulation means to control the signature of the synthetic target stream.
Gaffney U.S. Pat. No. 4,866,449 discloses a multi-channel alignment processor for signals modulated onto a common IF frequency for a monopulse radar. A/D and baseboard converter circuits 28, 32, 36 and 40 respond to clock signals from generator 42. Digital signals are produced representing the I and Q components of the corresopnding baseband signals. Alternate circuitry is disclosed.
Chang et al U.S. Pat. No. 5,077,562 discloses a digital beam-forming technique using temporary noise injection using relatively few small-scale A/D converters wherein the IF input signal is separated into baseboard in-phase and quadrature-phase components by an I/Q split network.
The remaining patent references are included for general background information.